Ultrasonic unit



11. uwscf: a

June 29, 1965 H. c. METTLER 3,191,913

ULTRASONIC UNIT Filed May '22, 1961 3,191,913 Patented June 29, 1965 ice3,191,913 ULTRASGNXC UNIT Hal C. Mettler, 1709 Putney Road, Pasadena,Calif. Filed hay 22, 1961, Ser. No. 111,617 Claims. (Cl. 259-72) Thisinvention relates to piezoelectricity and more particularly to animproved apparatus for developing mechanical vibrations using apiezoelectric crystal element.

The use of vibratory energy for drilling, routing, cleaning, etc. isgenerally known. For example, ultrasonic cleaning apparatuses aregenerally known which use a single frequency mechanical vibration forcleaning action. Usually ultrasonic cleaning apparatuses have a cleaningtank for holding a cleaning media or wetting agent. Objects to becleaned such as medical utensils, watch parts,

clothing, etc. are placed in the cleaning media. Mechanical vibratoryenergy is applied to the cleaning tank, v.wh"ch in turn sets upmechanical vibrations in.the"'cleaning media causing foreign particlesto bcarciiioved from the objects being cleaned.

The mechanical vibratory energy is generally developed by apiezoelectric crystal element. A piezoelectric crystal element is usedherein to refer to those crystals, such as Rochelle salt crystals andpolarized barium titanate crystals, which mechanically vibrate whensubjected to an electrical alternating current signal.

Piezoelectric crystals have resonant frequencies. Generally, usefulvibratory energy may only be obtained from piezoelectric crystals atthese resonant frequencies. In a parallelepiped piezoelectric crystalelement, for example, three resonant frequencies are found. Theseresonant frequencies are approximately proportional to the dimensionsbetween parallel surfaces of the crystal element.'

Piezoelectric crystal elements have generally been energized with asingle frequency electrical signal. The single frequency signal isapplied between parallel surfaces of the crystal element. The frequencyof the signal is equal to the resonant frequency of the crystal which isproportional to the dimension between the surfaces receiving theelectric signals. Problems which this method of energization create areexplained and eliminated in a co-pending application entitled UltrasonicCleaner bearing the'Serial No. 56,170 and tiled on September l5, 1960,now abandoned.

Generally, the vibratory energy available for 'cleaning action is low inultrasonic cleaners. The amount of vibratory energy developed may beincreased by increasing the amount of power applied to the crystalclement. However, crystals dissipate power and an increase in the powerapplied to the crystal element causes power dissipation in the crystalto increase. A laboratory test was performed on a priorv art cleaningapparatus using a parallelcpiped crystal element having resonantfrequencies at kilocycles, 40 kilocycles and 90 kilocycles. In the test,150 watts of power was first applied across the crystal element at 2Okilocycles and then at 40 kilocycles, At these frequencies, thevibratory energy applied to a live gallon cleaning tank by the crystalelement was far below that required for useful cleaning action.Subsequently, 150 watts of power was applied across the same crystalelcment at 90 kilocycles, At 9() kilocycles, the crystal elementoverheated, cracked and became useless.

To reduce the amount of power loss in each crystal, a group of crystalshave been connected in parallel. This again increases the expense of theultrasonic cleaning unit due to the expense of the crystal elements.

Another method used to reduce the amount of power loss in each crystalis to add a large metallic heat sink to the crystal. However, this againincreases the cost of the ultrasonic cleaner.

'"ciently at higher frequencies.

Previously, ultrasonic cleaners have been extremely sensitive todilferences in loading. Therefore, Whenever the liquid level in thecleaning tank or weight of objects being cleaned were changed, thefrequency of energization had to be vreadjusted. This has been correctedin some instances by feedback circuits. However, this reduces theavailable power for cleaning action and is expensive.

Dead spots are found in the cleaning media of prior ultrasonic cleaningunits. At these dead spots, very little useful vibratory energy isavailable for cleaning action. It has also been found that the cleaningaction in prior known cleaners is the greatest at the center of thecleaning media in the cleaning tank and that around the outer edges ofthe cleaning media, the cleaning action is quite low.

Soft objects are cleaned most eliiciently at lower frequencies, whereasharder objectsare cleaned most effi- Thus, prior known ultrasoniccleaning apparatus must provide means for energizing crystal elementsseparately at low frequencies for cleaning soft objects and at highfrequencies for cleaning hard objects. The apparatus for this method ofenergization is expensive and separate steps are required for cleaninghard and soft objects. Also, these ultrasonic cleaners must be tuned andswitched to two different frequencies.

Briefly, one embodiment of the present invention provides an ultrasoniccleaning unit with a piezoelectric crystal element having twoharmonically related resonant frequencies. The piezoelectric crystal isin the shape of a parallelepiped.

An inductive impedance element is connected in parallel with the crystalelement across two of its parallel surfaces. There is a de-energizedvalue of capacitance across the two parallel surfaces of the crystalelement. The inductance of the inductive element is adjusted relative tothis capacitance such that the combination provides a tuned tank circuitwith a resonant frequency equal to the mean value of the two resonantfrequencies of the crystal element. An oscillator circuit is providedfor developing a high frequency signal the frequency of which issubstantially equal to that of one of the harmonically related resonantfrequencies of the crystal element. An amplifier is used to couple thehigh frequency signals from the oscillator to the crystal element. Thiscauses the crystal element to simultaneously mechanically vibrate atboth the harmonically related resonant frequencies of the crystalelement.

In the above-mentioned laboratory tests on the prior art cleaningapparatus, a piezoelectric crystal element having resonant frequenciesof 20 kilocycles, 40 kilocycles and kilocycles was tested in anembodiment of the present invention. The oscillator circuit was set toprovide signals at a frequency of 20 kilocycles and the inductiveelement was adjusted to provide a resonant circuit at 30 kilocycles. Thecrystal element was energized with 150 watts of power. The crystalclement was found to be so ctlicient that at 7()Q F. ambienttemperature, the ternperature of the crystal only rose to about to 113F. indicating an extremely low power loss. ln addition, a uniformcleaning action was noted throughout the entire cleaning media in thetank.

During the tests on the embodiment of the present invention, it was alsofound that the ratio of the peak instantaneous power to average powerdelivered to the crystal element was about 27 to l. This is in contrastto prior art cleaning apparatuses where this same ratio was about 4 tol. lt is extremely important to keep the ratio of peak instantaneouspower to average power as high as possible because the peak powerprovides the actual cleaning action whereas the average power just heatsup the crystal and attached structure. It was also found that theultrasonic cleaning unit is virtually independent of loading andreturning is not required as the load changes. Additionally hard andsoft objects may be cleaned at the same due to the simultaneous high andlow frequencies of vibration. The invention disclosed in this patentapplication is an improvement over the invention described and claimedin a co-pending patent application, Serial No. 56,170 filed September15, 1960, now abandoned, which was re-tiled as a continuing patentapplication on July 5, 1963, bearing the Serial No. 294,223.

A better understanding of the present invention may be had withreference to the following detailed description and tigures, in which:

FIGURE 1 is a perspective view partially broken away of an ultrasoniccleaning unit and embodying the present invention;

FIGURE 2 is a schematic-block diagram of the electrical circuits of FIG.l;

FIGURE 3A is a perspective view of a parallelepipedY piezoelectriccrystal element for use in the ultrasonic cleaning unit of FIG. 1;

FIGURE 3B is atable showing the resonant frequencies and the dimensionsof the piezoelectric crystal element of FIG. 3A; and

FIGURE 4 is a wave shape diagram showing the power wave form applied tothe crystal element of FIG. 3A during operation.

Refer now to FIG. 1. FIGURE 1 shows an ultrasonic cleaning unit. Thecleaning unit comprises a metallic container unit or cleaning tank 10having a cavity in which a cleaning solution or other cleaning media 12,such as water, is placed. Objects to be cleaned are placed in thesolution 12 within the cavity. A piezoelectric crystal element 14 isattached to the bottom of the cavity. A source of electric signals 16for energizing the piezoelectric crystal element 14 is located at oneend of the cleaning tank 10. The source 16 provides high frequencyelectrical signals to the crystal element 14 causing the crystal element14 to vibrate the cleaning tank 10. The vibration energy set up in thecleaning tank 10 in turn causes vibration energy throughout the cleaningmedia 12 causing foreign particles to be removed from objects placed inthe cleaning media 12.

Refer now to FIG. 3A. FIGURE 3A shows the crystal element 14 and aportion of the bottom of the cavity of the cleaning tank 10. The crystalelement 14 is in the shape of a parallelepiped. The parallel surfacesare separated by the dimensions represented by the symbols 20, 21 and22. Corresponding to the dimensions 20, 21 and 22, the crystal element14 has three resonant frequencies represented by the symbols f1, f2 andf3, respectively. The

parallel surfaces separated by the dimension 22 have metallic surfacesor electrodes 18. The metallic surfaces 18 may be conductors such assilver which is plated or sprayed on the Surfaces by means of a numberof wellknown processes. One of the metallic surfaces 18 is connected tothe bottom of the cavity by means of a nonhardening cement, or othermeans which will not deteriorate or break loose due to mechanicalvibrations in the crystal element 14.

FIGURE 3B shows the values of the resonant frequencies f1, f2 and f3 andthe corresponding dimensions of the crystal element of FIG. 4. Asindicated, the three frequencies, f1, f2 and f3, are equal to 40kilocycles, 20 kilocycles and 90 kilocycles, respectively. It should benoted at this point that the frequencies f1 and f2 are harmonicallyrelated to each other. Also, the frequency f2 is the fundamentalfrequency and the frequency indicated by the symbol f1 is the secondharmonie frequency of the primary frequency f2. A typical bariumtitanate crystal element having these resonant frequencies has thedimensions 20, 21 and 22 equal to two and One-quarter inches, four andthree-eighths inches and one and one-sixteenth inches, respectively,indicated in FIG. 3B.

With the general arrangement of the ultrasonic cleaner of FIG. l in mindand the details of the dimensions and resonant frequencies of thecrystal element 14 of FIG. 3A in mind, refer generally to theschematic-block diagram of FIG. 2. A source of signals or an oscillatorcircuit 30 is provided for developing high frequency signals. Anamplitier circuit 28 couples the signals from the oscillator circuit 30to a tuned tank circuit 26. A power supply 32 provides power to thetuned tank circuit 26 and the amplier 28.

The oscillator 30 is a conventional type tuned grid tuned plateoscillator generally known in the electronics art. The tuned grid tunedplate oscillator 30 provides output signals having a frequency equal toone of the resonant frequencies of the crystal element 14. In FIG. 2,the frequency of the output signal from the oscillator 30 is equal to 20kilocycles which is the frequency of the lower of the two harmonicallyrelated resonant frequencies of the crystal 14.

The amplifier circuit 28 comprises a conventional heated cathode type oftriode vacuum tube 34 having its grid electrode connected through aparasitic suppressor resistor 35 to the output circuit of the oscillatorcircuit 30. The cathode electrode of the vacuum tube 34 is connected toa filament power supply in the power supply 32. The signals to theamplifier circuit 28 are such that the vacuum tube 34 is operated inclass C.

The tuned tank circuit 26 comprises the piezoelectric crystal element 14connected in parallel with an inductive impedance element 36. Thesurfaces 18 of the piezoelectric crystal element 14 are connected to twolead wires 24 and 25. The lead wire 25 is connected to ground (zerovolts potential). The lead wire 24 is connected to one end of theinductive impedance element 36 and a plate of the vacuum tube 34. Theother end of the inductive impedance element 36 is connected to theplate power supply in the power supply 32. The piezoelectric crystalelement 14 has a predetermined value of capacitance between the surfacescoated with the metallic electrodes 18. Also, the inductive impedanceelement 36 has a certain value of inductance. The ratio of theinductance of the impedance element 36 to the capacitance of thepiezoelectric crystal element 14 is such that the tuned tank circuit 26has a resonant frequency equal to 30 kilocycles, exactly equal to themean of the harmonically related resonant frequencies 40 kilocycles and20 kilocycles.

Tests were performed on an ultrasonic cleaning unit having theelectrical components shown in FIG. 2. In the tests, the dualfrequencies of 20 kiloeycles and 40 kilocycles were observed and thepeak power applied to the crystal element was measured. This test wasperformed using a dual trace oscilloscope and observing both the currentand voltage wave form through the crystal element 14. The oscilloscopewas calibrated so that both l voltage and current had the same peakamplitude. Voltage and current were found to be essentially in phase.FIGURE 4 shows the wave shape of the power applied across the crystalelement 14 during this test. As indicated, the peak value of the powerdelivered to the crystal element is about 4,000 watts and the averagepower very much lower. f

It should be understood that the present invention is not restricted tothat shown in the drawings but other circuit arrangements may be devisedand yet come within the present invention as defined by the claims. Forexample, the harmonically resonant frequencies of the crystal elementare not restricted to first and second harmonics but other harmonicallyrelated frequencies may be used. Also, the frequency developed by theoscillator 30 may be equal to the upper harmonically related frequencyrather than the lower. The resonant frequency is not restricted to themean frequency but may be other values in between the upper and lowerharmonically related frequencies.

It should also be understood that the crystal element 14 may besimultaneously energized at all three resonant frequencies at once byusing a crystal element having a third frequency f3 that is in harmonicrelation to the other resonant frequencies f1 and yzj Also a pluralityof crystal elements may be used rather than just one.

The present invention is not limited to an ultrasonic cleaning unit butmay be incorporated in ultrasonic or vibrating drilling or routingapparatus or other apparatus using mechanical vibratory energy.

What is claimed is:

1. A vibratory cleaning unit the combination comprising a cleaning tank,a piezoelectric crystal element mounted for providing mechanicalvibratory energy to said cleaning tank, said piezoelectric crystalelement having dimensions determinative of at least two harmonicallyrelated resonant vibrating frequencies and a pair of surfaces forreceiving electrical energy having a predetermined value of capacitancetherebetween, means for forming an energizing signal for said crystalelement having a substantially constant frequency substantially equal toone of said harmonically related frequencies and an inductive impedanceelement arranged having a value of inductance relative to said value ofcapacitance and coupled across said pair of surfaces for causing saidcrystal element to simultaneously vibrate at both said harmonicallyrelated frequencies for providing substantially uniform cleaning actionto the cleaning tank with changes in loading in the cleaning tank.

2. In a mechanical vibratory energy generating apparatus thecombination, comprising:

a piezoelectric crystal element having dimensions determinative of atleast two harmonically related resonant mechanical vibratory frequenciesof the crystal, and means for applying an energizing signal to thecrystal element having at least two frequency components substantiallyequal to said two harmonically related resonant vibratory frequencies,said energizing means being adapted for applying an energizing signal ofsulicient power at both of said frequencies for causing the crystalelement to form mechanical vibratory power at both said harmonicallyrelated resonant vibratory frequencies.

3. In a mechanical vibratory energy generating apparatus thecombination, comprising:

a piezoelectric crystal element arranged for forming mechanicalvibratory energy and having dimensions determinative of at least twoharmonically related resonant vibratory frequencies, means for applyingan energizing signal to the crystal element having a frequencysubstantially equal to one of said harmonically related resonantvibratory frequencies, and means comprising an inductive impedancecoupled to the crystal element and adapted for causing the crystalelement to form mechanical vibratory power, in response to saidenergizing signal, having frequency components substantially equal toboth of said harmonically related vibratory frequencies.

4. A mechanical vibratory energy generating apparatus the combination,comprising:

a piezoelectric crystal element having dimensions determinative of atleast two harmonically related resonant mechanical vibratoryfrequencies, a source of alternating current signals having a frequencysubstantially equal to one of said harmonically related resonantmechanical vibratory frequencies, first means responsive to thealternating current signal for applying an energizing signal across thecrystal element, and second means comprising an inductive impedancecoupled to the crystal element and adapted for causing the crystalelement to form vibratory power, in response to said energizing signal,having frequency components substantially equal to both saidharmonically related resonant vibratory frequencies, said Iirst meansadditionally comprising isolation means adapted for substantiallyisolating eleccomprising said inductive impedance means from the signalsource.

5. A mechanical vibratory energy generating apparatus the combination,comprising:

a piezoelectric crystal element having dimensions determinative of atleast two harmonically related resonant mechanical vibratoryfrequencies, a source of alternating current signals having a frequencysubstantially equal to the lower one of said harmonically relatedresonant mechanical vibratory frequencies, first means responsive to thealternating current signal for applying an energizing signal across thecrystal element, and second means comprising an inductive impedancecoupled to the crystal element and adapted for causing the crystalelement to form vibratory power, in response to said energizing signal,having frequency components substantially equal to both saidharmonically related resonant vibratory frequencies, said first meanscomprising isolation means for substantially isolating electricalsignals formed by the crystal and said inductive impedance means fromthe signal source.

6. A mechanical vibratory energy generating apparatus the combination,comprising:

a piezoelectric crystal element having dimensions determinative of atleast two harmonically related resonant mechanical vibratoryfrequencies, one of said resonant mechanical vibratory frequencies beingsub- Vstantially twice the other, a source of alternating currentsignals having a frequency substantially equal to the lower one of saidharmonically related resonant mechanical vibratory frequencies, firstmeans responsive to the alternating current signal for applying anenergizing signal across the crystal element, and second meanscomprising an inductive impedance coupled to the crystal element andadapted for causing the crystal element to form vibratory power, inresponse to said energizing signal, having components substantiallyequal to both said resonant frequencies, said irst means comprisingisolation means for substantially isolating electrical signals formed bythe crystal and said means comprising said inductive impedance meansfrom the signal source.

7. A mechanical vibratory energy generating apparatus the combination,comprising:

a piezoelectric crystal element arranged for forming mechanicalvibratory energy and having at least two substantially fiat parallelsurfaces having metallic surfaces thereon with a predetermined value ofcapacitance therebetween and including dimensions determinative of atleast two harmonically related resonant mechanical vibratoryfrequencies, a source of alternating current signals having a frequencysubstantialy equal to the lower one of said harmonically relatedmechanical vibratory frequencies, means responsive to the alternatingcurrent signals for applying an electrical energizing signal ofsubstantially the same frequency across the metallic surfaces on saidcrystal element, and an inductive impedance element electrically coupledin parallel with the energizing signal across the metallic surfaces andhaving a value of inductance such that together with said capacitance atuned circuit is formed having a resonant frequency substantially equalto the mean frequency of said harmonically related vibratory frequenciesand thereby cause the crystal element to form vibratory power, inresponse to said electrical energizing signal, having frequencycomponents substantially equal to both of said harmonically relatedmechanical vibratory frequencies, said energizing signal meanscomprising isolation circuit means for substantially isolatingelectrical signals formed in the tuned circuit from the signal source.

8. A mechanical vibratory energy generating apparatrical signals formedby the crystal and said means tus as defined in claim 7 wherein one ofthe resonant mechanical vibratory frequencies of the crystal element issubstantially double the other resonant mechanical vibratory frequency,and wherein said isolation circuit means comprises a vacuum tube coupledbetween the crystal element and energizing signal means including aplate circuit coupled to the crystal element and a grid circuit coupledto the energizing signal means.

9. In a mechanical vibratory cleaning apparatus the combination,comprising:

a cleaning tank, a piezoelectric crystal element mounted for providingvibrating energy to the cleaning tank and having dimensionsdeterminative of at least two harmonically related resonant mechanicalvibratory frequencies, a source of alternating current signals having afrequency substantially equal to the lower one of said harmonicallyrelated resonant mechanical vibratory frequencies, rst means responsiveto said alternating current signals for applying an energizing signalacross the crystal element of substantially the same frequency, andsecond means comprising an inductive impedance coupled to the crystalelement and adapted for causing the crystal element to mechanicallyvibrate and apply mechanical vibratory power to the cleaning tank havingfrequency components substantially equal to both of said harmonicallyrelated resonant mechanical vibratory frequencies, said rst meanscomprising isolation circuit means for substantially isolatingelectrical signals formed by the crystal and said inductive impedancemeans from the signal source.

10. In a mechanical vibratory cleaning apparatus the combination,comprising:

a cleaning tank, having a bottom and sides, a piezoelectric crystalelement for providing mechanical vibratory energy to the cleaning tankand having at least two substantially tlat parallel surfaces havingmetallic surfaces thereon with a predetermined value of capacitancetherebetween, the crystal element having dimensions determinative of atleast two harmonically related resonant mechanical vibratory frequenciesone of which is substantially twice the other, the crystal being mountedon said tank with said parallel surfaces and said dimensions positionedsubstantially parallel with the bottom of said tank, a constantfrequency oscillator circuit for forming a signal having a frequencysubstantially equal to the lower one of said harmonically relatedresonant vibratory frequencies, an electrical circuit arranged to beresponsive to the oscillator signal for applying an energizing signalacross the metallic surfaces of said crystal element of substantiallythe same frequency, and an inductive impedance element coupled inparallel with the energizing signal across the metallic surfaces andhaving a value of inductance such that together with the capacitance atuned circuit is formed having a resonant frequency approximately equalto the mean frequency of said vibratory frequencies for causing thecrystal element to provide sharp peaks of substantially uniformmechanical vibratory power throughout any cleaning liquid placed in thecleaning tank having frequency components substantially equal to both ofsaid harmonically related mechanical vibratory frequencies, saidelectrical circuit comprising a vacuum tube having a plate circuitcoupled to one of the surfaces of the crystal element and a grid circuitcoupled to the oscillator circuit for substantially isolating electricalsignals formed in the tuned circuit from the oscillator circuit.

References Cited by the Examiner UNlTED STATES PATENTS 1/50 Spanier68-20 5/53 Harvey C310-8.2 11/54 Donley S10-8.2 6/59 Branson z- S10- 8.15/60 Welkowitz et al. 3 lO-9.4

FOREIGN PATENTS 8/ 5 8 Canada.

CHARLES A. WILLMUTH, Primary Examiner.

LEO QUACKENBUSH, Examiner.

2. IN A MECHANICAL VIBRATORY ENERGY GENERATING APPARATUS THECOMBINATION, COMPRISING: A PIEZOELECTRIC CRYSTAL ELEMENT HAVINGDIMENSIONS DETERMINATIVE OF AT LEAST TWO HARMONICALLY RELATED RESONANTMECHANICAL VIBRATORY FREQUENCIES OF THE CRYSTAL, AND MEANS FOR APPLYINGAN ENERGIZING SIGNAL TO THE CRYSTAL ELEMENT HAVING AT LEAST TOWFREQUENCY COMPONENTS SUBSTANTIALLY EQUAL TO SAID TWO HARMONICALLYRELATED RESONANT VIBRATORY FREQUENCIES, SAID ENERGIZING MEANS BEINGADAPTED FOR APLYING AN ENERGIZING SIGNAL OF SUFFICIENT POWER AT BOTH OFSAID FREQUENCIES FOR CAUSING THE CRYSTAL ELEMENT TO FORM MECHANICALVIBRATORY POWER AT BOTH SAID HARMONICALLY RELATED RESONANT VIBRATORYFREQUENCIES.